Nickel-promoted mesoporous ZSM5 for carbon monoxide methanation

Abstract

Nickel-promoted mesoporous ZSM5 (Ni/mZSM5) was prepared for CO methanation. XRD, NMR and SEM analysis confirmed the structural stability of Ni/mZSM5 with coffin type morphology. The nitrogen physisorption and pyrrole adsorbed FTIR analyses indicated the presence of micro–mesoporosity and a moderate amount of basic sites on both mZSM5 and Ni/mZSM5. At 623 K, Ni/mZSM5 showed a high rate of CO conversion (141.6 μmol CO g-cat⁻¹ s⁻¹) and 92% CH₄ yield. Ni/mZSM5 showed better catalytic performance than Ni/MSN (82.4 μmol CO g-cat⁻¹ s⁻¹, 82% CH₄ yield), Ni/HZSM5 (29.0 μmol CO g-cat⁻¹ s⁻¹, 54.5% CH₄ yield), and Ni/γ-Al₂O₃ (14.5 μmol CO g-cat⁻¹ s⁻¹, 38.6% CH₄ yield). It is noteworthy that the superior catalytic performance of Ni/mZSM5 could be attributed to the presence of both micro–mesoporosity and basicity, which led to a synergistic effect of Ni metal active sites and the mZSM5 support. In situ FTIR spectroscopy showed that CO and H₂ may be adsorbed on Ni metal followed by spillover to form adsorbed CO and adsorbed H on the mZSM5 surface. Then, two possible mechanisms for CO methanation were proposed. In the first mechanism, the adsorbed CO may be reacted with H₂ to form CH₄ and H₂O. In the second mechanism, the adsorbed H may be reacted with CO to form CH₄ and CO₂. However, in this case, the former is the predominant pathway as the methanation reaction is favored by inhibition of the water–gas shift reaction.